THE LIFE CYCLE 



91 



In a few days it molts, or casts its outer skin (not the 

 true skin, but a thin, firm covering or outer body wall com- 

 posed of a substance called chitin, which is secreted by the 

 cells of the true skin). In this second larval stage there 

 can be seen the rudiments of four wings, in .the condition 



FIG. 42. Post-embryonic development (incomplete metamorphosis) of the Rocky 

 Mountain locust (Melanoplus spretus). a, b, c, d, e, and /, successive develop- 

 mental stages from just hatched to adult individual. After EMERTON. 



of tiny wing pads on the back of the middle part of the 

 body (the thorax). Soon the chitinous body covering is 

 shed again, and after this molt the wing pads are mark- 

 edly larger than before. Still another molt occurs, with 

 another increase in size of the developing wings, and after 

 a fifth and last molt the wings are fully developed, and 



